Present technology consists in mounting normally up to eight knife holders onto the peripheral flat faces of a solid polygonal core, which is itself keyed to a motorized rotating shaft.
The shape of the knife holder presently utilized is generally that of a four-sided open-ended box of which the bottom side is affixed to a face of the polygonal core and the top side serves as a mounting surface for the cutter knife.
Such arrangement causes the chips produced by the knife to pass through the box and, upon ejecting at the rear end, to meet the forward edge of the outside wall of the next incoming knife holder. At this point, part of the chips produced by the preceding knife will deflect outside of the circular orbit of the knives and holders, while some chips will engage into the tunnel arrangement of the next holder and even repeat the process to the point of being carried back to the cutting area where they were produced. Therefore, any recutting of existing chips or impact with holder walls, are greatly detrimental to chip quality because of splintering of the wood fibres.
Given the present design of knife holders, attempts have been made to minimize chip quality downgrading by increasing the distance between the knife holders so as to facilitate the chip escape outside the path of incoming knife holders. This has resulted in providing larger diametrical head dimensions. However, by thus increasing the cutting circle, the knife cutting velocity becomes higher which, in turn, causes more severe knife impact on the wood and additional fibre splintering, specially under frost conditions.
It is known in the chip making technology that the cutter head RPM is related only to feed rate, the number of cutter knives and the required chip length. Assuming constant values for these three factors, any change in the cutting circle diameter directly affects the knife velocity and impact on the wood since no change in RPM occurs.